Water used for industrial purposes typically comprises various impurities at low concentrations. Some impurities pose little or no hindrance to the industrial water process, while others can cause inefficiencies. The typical industrial water user may lessen or prevent the inefficiencies caused by known impurities by employing one or more water treatment schemes. For example, possible treatment schemes may include those described in U.S. Pat. Nos. 4,457,847; 4,545,920; 4,711,726; 5,736,405; 5,041,386; 5,384,050; 6,566,139; 6,436,711; 6,587,753; 6,336,058; 7,220,382; 7,448,255; 7,951,298; 7,955,853; and 8,068,033; and U.S. Patent Application Publication Nos. 2008/0202553 and 2008/0179179, the disclosures of each are herein incorporated by reference in their entirety.
Two impurities that may be present in water are soluble calcium and soluble magnesium, commonly known as “hardness.” Water may be described as “soft,” i.e., generally containing little or no soluble calcium or magnesium; or “hard,” i.e., generally having higher (and sometimes undesirably high) concentrations of soluble calcium, soluble magnesium, or both. Hard water can cause known problems in industrial water systems, particularly in thermal industrial water systems, and more particularly in heated thermal industrial water systems such as boiler systems. Some of these known problems may be initiated by concentrations of soluble calcium, soluble magnesium, or both that are not especially high.
Hard water can be softened using one or more water softening procedures, which may include purification using physical or chemical treatment. Non-limiting examples of physical treatment include filtration; distillation; membrane purification including reverse osmosis, forward osmosis, membrane filtration (microfiltration, ultrafiltration, etc.), membrane distillation; ion exchange; and electrochemical methods to precipitate scale. Non-limiting examples of chemical treatment include chelation using at least one chelant such as ethylenediamine tetraacetic acid (“EDTA”) or a salt thereof, or precipitation using one or more caustic and/or phosphate compound.
Various analytical methods can be employed to measure hardness in water entering, re-entering, or being used in an industrial process (hereinafter “industrial water”). Hardness concentrations can be measured by inductively coupled plasma (“ICP”), ion selective electrode (“ISE”), light absorbance, titration, atomic absorption (“AA”), or other methods known in the art. While all can produce accurate hardness concentration measurements, each has limitations.